Thyroid function and psychiatric morbidity in patients with manic disorder receiving lithium therapy

Area of Science:

• Endocrinology
• Psychiatry
• Pharmacology

Background:

• Euthyroid hyperthyroxinemia, characterized by elevated free thyroxine (FT4) and free triiodothyronine (FT3) despite normal thyroid-stimulating hormone (TSH), is hypothesized to contribute to manic disorder.
• Lithium, a common treatment for bipolar disorder, exhibits a potent short-term antithyroidal effect, which may underlie its antimanic action.

Purpose of the Study:

• To prospectively investigate the relationship between thyroid function and psychiatric morbidity in patients with manic disorder.
• To assess the impact of lithium treatment on thyroid hormone levels and psychiatric symptoms.

Main Methods:

• Prospective assessment of thyroid function (FT4, FT3, TSH) and psychiatric status in 46 adult patients with manic disorder before and 1, 6 months after initiating lithium treatment.
• Correlation analyses and multilevel modeling were used to examine associations between thyroid hormone levels, lithium levels, and psychiatric symptom scores (Brief Psychiatric Rating Scale, Global Assessment Scale).

Main Results:

• At baseline, patients exhibited FT4 levels at the high end of the normal range, with 11% showing elevated FT4. Baseline FT3 and FT4 correlated positively with past psychiatric morbidity.
• Lithium treatment led to a significant reduction in FT3 and FT4 levels within the first month, which correlated with decreased psychiatric symptoms. FT4 remained significantly lower at 6 months, while TSH progressively increased.
• Higher FT4 levels and lower serum lithium levels were associated with increased psychiatric symptoms.

Conclusions:

• The findings support the hypothesis that euthyroid hyperthyroxinemia contributes to acute mania.
• Lithium's short-term antimanic efficacy may be partially mediated by its antithyroid effect, specifically by reducing FT4 levels.